Message text written by "R. Ashford Little II"
>I've done some investigating and am only further confused (my wife would
>argue this is a permanent state of mind).
Mine says the same about me.
>1. I took the DPWA switch off and looked at the piston and you really
>can't tell much since the hole is so small.
You need a good light and look for a reduced diameter in the plunger. But
leave that for now.
>2. I disconnected the brake pipe at the reservoir for the rear brakes
>(small res) and fluid flowed out when the pedal was pumped. This fluid
>however depleted the front brake reservoir and yes the pipes aren't
>switched.
The master cylinder is constructed as a duplex device that has a main
piston that operates in the Front Brake portion fo the bore. There is also
a floating piston that separates the front brakes and rear brakes portions.
When you step on the brake pedal you push the first piston that dies
several things. 1) it closes the tipping valve closing off access to the
reservoir, 2) creates pressure causing brake fluid to flow to the front
calipers and 3) creates pressure causing the floating piston to move and
3A) close off the reservoir and 3B) create pressure to cause fluid to flow
to the rear wheel cylinders.
The floating piston serves as an interface between the two circuits. If
the rubber cup were to allow fluid to pass then you can get flow from the
front brake reservoir to the rear brake circuit. If this is the case then
your master cylinder needs attention.
>3. I disconnected the inboard pipe from the DPWA and fluid also flowed
>from that hole as well and it was also front brake fluid.
>
>At no time have I been able to drain or deplete the fluid level for the
>rear brakes.
Another reason to service the master cylinder
>Initially I though that the DPWA might be the culprit, but I can see no
>logical reason for front disc fluid to flow out of the hole directly
>below the rear drum reservoir or for front disc fluid to flow out of the
>rear drum DPWA hole.
Exactly!
>If the master is bad, then why would fluid flow out of the rear DPWA
>hole in the DPWA?
The fault at the master cylinder doesn't prevent fluid flowing out of the
rear brake circuit. The fault is internal and determines from whence the
fluid comes.
>Hmmmm? And to think I only started out to change the four brake
>lines....
Better to catch it now than on the road.
It also concievable that the PO (previous owner) had been in the master
cylinder and had left out the floating piston. In order to make this work
he would have to plug the port to the smaller reservoir. This is
consistent with yoru symptoms. But there can be a less sinister cause.
Just keep in mind just how important your brakes are.
Good Luck
Dave
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